More than 250,000 people – twice the expected number – participated in the biggest mass birdwatch in the gardens, parks and schoolgrounds of Britain at the end of January.

But the results of the Big Garden Birdwatch provided a depressing reminder of the continuing decline of Britain's most common birds, the starling and the house sparrow.

Although more of these species were spotted – 700,000 and 673,000 respectively - well ahead of the blue tit in the No 3 spot on 455,000, the survey shows starling numbers have dropped by 70 per cent and house sparrows by 57 per cent since 1979. Both are candidates for the official red list of species of conservation concern. Garden Birdwatch, organised annually for the past 23 years by the Royal Society for the Protection of Birds, has monitored their decline.

The figures tally with the evidence produced by The Independent's two-year campaign to find a cause for the sparrow slump, particularly in urban centres, their former strongholds. In a classic example, in Kensington Gardens, London, only 12 were counted in the summer of 2000, compared with 2,603 in 1925.

Also in the summer of 2000, checks in the centre of Sunderland found only eight sparrows – yet in the RSPB survey 56 were counted in one garden just five miles away at the village of Whitburn, highlighting the stark contrast between city centres and semi-rural areas on their outskirts. Richard Bashford, the survey co-ordinator, said such results confirmed the disappearance of sparrows from population centres.

Despite the bad news, he was delighted with the response of the public. "More than a quarter of a million people was far beyond what we hoped to achieve – it was a fantastic response, demonstrating the extent of public interest in birds. Also with over 4 million birds counted nationally, it shows how important gardens are to wildlife – add them all together and we have a quite considerable nature reserve."

Unlike sparrows and starlings, some species are increasing in numbers. The garden populations of collared doves – which only colonised Britain in the 1950s – were the seventh most commonly seen species and the woodpigeon ninth. Populations have increased by 500 per cent since the survey began. Milder winters are given as the reason for the 150 per cent increase in the numbers of wrens since 1979.

Blackbirds were found to be the most widespread UK garden birds, cropping up in 89 per cent of all gardens, and other similar areas, covered by the survey. However, the distribution maps show lower numbers in more westerly and southerly parts of the country – probably a reflection of greater breeding success in eastern regions.

Most common garden birds

1) Starling: More than 700,000 counted but the starling population is down by 70 per cent since 1979.

2) House sparrow: 673,000. Numbers have fallen almost as sharply as starling (57 per cent).

3) Blue tit: 455,000. Found to be in particular decline in Scotland and Northern Ireland.

4) Blackbird: Spotted the length and breadth of the United Kingdom. 411,000 recorded.